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Author name code: scullion
ADS astronomy entries on 2022-09-14
author:"Scullion, Eamon"
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Title: Small-scale solar jet formation and their associated waves
and instabilities
Authors: Skirvin, Samuel; Verth, Gary; Juan González-Avilés, José;
Shelyag, Sergiy; Sharma, Rahul; Guzmán, Fransisco; Ballai, Istvan;
Scullion, Eamon; Silva, Suzana S. A.; Fedun, Viktor
2022arXiv220509598S Altcode:
Studies on small-scale jets' formation, propagation, evolution,
and role, such as type I and II spicules, mottles, and fibrils in
the lower solar atmosphere's energetic balance, have progressed
tremendously thanks to the combination of detailed observations and
sophisticated mathematical modelling. This review provides a survey of
the current understanding of jets, their formation in the solar lower
atmosphere, and their evolution from observational, numerical, and
theoretical perspectives. First, we review some results to describe
the jet properties, acquired numerically, analytically and through
high-spatial and temporal resolution observations. Further on, we
discuss the role of hydrodynamic and magnetohydrodynamic instabilities,
namely Rayleigh-Taylor and Kelvin-Helmholtz instabilities, in jet
evolution and their role in the energy transport through the solar
atmosphere in fully and partially ionised plasmas. Finally, we discuss
several mechanisms of magnetohydrodynamic wave generation, propagation,
and energy transport in the context of small-scale solar jets in
detail. This review identifies several gaps in the understanding of
small-scale solar jets and some misalignments between the observational
studies and knowledge acquired through theoretical studies and numerical
modelling. It is to be expected that these gaps will be closed with
the advent of high-resolution observational instruments, such as
Daniel K. Inouye Solar Telescope, Solar Orbiter, Parker Solar Probe,
and Solar CubeSats for Linked Imaging Spectropolarimetry, combined
with further theoretical and computational developments.
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Title: Implications of spicule activity on coronal loop heating and
catastrophic cooling
Authors: Nived, V. N.; Scullion, E.; Doyle, J. G.; Susino, R.; Antolin,
P.; Spadaro, D.; Sasso, C.; Sahin, S.; Mathioudakis, M.
2022MNRAS.509.5523N Altcode: 2021arXiv211107967N; 2021MNRAS.tmp.3004N
We report on the properties of coronal loop foot-point heating
with observations at the highest resolution, from the CRisp Imaging
Spectro-Polarimeter located at the Swedish 1-m Solar Telescope and
co-aligned NASA Solar Dynamics Observatory observations, of Type II
spicules in the chromosphere and their signatures in the extreme
ultraviolet (EUV) corona. Here, we address one important issue,
as to why there is not always a one-to-one correspondence, between
Type II spicules and hot coronal plasma signatures, i.e. beyond
TR temperatures. We do not detect any difference in their spectral
properties in a quiet Sun region compared to a region dominated by
coronal loops. On the other hand, the number density close to the
foot-points in the active region is found to be an order of magnitude
higher than in the quiet Sun case. A differential emission measure
analysis reveals a peak at ~5 × 10<SUP>5</SUP> K of the order of
10<SUP>22</SUP> cm<SUP>-5</SUP> K<SUP>-1</SUP>. Using this result as
a constraint, we conduct numerical simulations and show that with an
energy input of 1.25 × 10<SUP>24</SUP> erg (corresponding to ~10 RBEs
contributing to the burst) we manage to reproduce the observation very
closely. However, simulation runs with lower thermal energy input do not
reproduce the synthetic AIA 171 Å signatures, indicating that there
is a critical number of spicules required in order to account for the
AIA 171 Å signatures in the simulation. Furthermore, the higher energy
(1.25 × 10<SUP>24</SUP> erg) simulations reproduce catastrophic cooling
with a cycle duration of ~5 h, matching a periodicity we observe in
the EUV observations.
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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
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Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.
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Title: 2D and 3D Analysis of a Torus-unstable Quiet-Sun Prominence
Eruption
Authors: Rees-Crockford, T.; Bloomfield, D. S.; Scullion, E.; Park,
S. -H.
2020ApJ...897...35R Altcode:
The role of ideal-MHD instabilities in a prominence eruption is
explored through 2D and 3D kinematic analysis of an event observed
with the Solar Dynamics Observatory and the Solar Terrestrial Relations
Observatory between 22:06 UT on 2013 February 26 and 04:06 UT on 2013
February 27. A series of 3D radial slits are used to extract height-time
profiles ranging from the midpoint of the prominence leading edge to
the southeastern footpoint. These height-time profiles are fit with a
kinematic model combining linear and nonlinear rise phases, returning
the nonlinear onset time (t<SUB>nl</SUB>) as a free parameter. A
range (1.5-4.0) of temporal power indices (I.e., β in the nonlinear
term ${(t-{t}_{\mathrm{nl}})}^{\beta }$ ) are considered to prevent
prescribing any particular form of nonlinear kinematics. The decay
index experienced by the leading edge is explored using a radial
profile of the transverse magnetic field from a PFSS extrapolation
above the prominence region. Critical decay indices are extracted for
each slit at their own specific values of height at the nonlinear
phase onset (h(t<SUB>nl</SUB>)) and filtered to focus on instances
resulting from kinematic fits with ${\chi }_{\mathrm{red}}^{2}\lt 2$
(restricting β to 1.9-3.9). Based on this measure of the critical
decay index along the prominence structure, we find strong evidence
that the torus instability is the mechanism driving this prominence
eruption. Defining any single decay index as being "critical" is not
that critical because there is no single canonical or critical value
of decay index through which all eruptions must succeed.
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Title: Velocity Response of the Observed Explosive Events in the
Lower Solar Atmosphere. I. Formation of the Flowing Cool-loop System
Authors: Srivastava, A. K.; Rao, Yamini K.; Konkol, P.; Murawski,
K.; Mathioudakis, M.; Tiwari, Sanjiv K.; Scullion, E.; Doyle, J. G.;
Dwivedi, B. N.
2020ApJ...894..155S Altcode: 2020arXiv200402775S
We observe plasma flows in cool loops using the Slit-Jaw Imager on board
the Interface Region Imaging Spectrometer (IRIS). Huang et al. observed
unusually broadened Si IV 1403 Šline profiles at the footpoints of
such loops that were attributed to signatures of explosive events
(EEs). We have chosen one such unidirectional flowing cool-loop
system observed by IRIS where one of the footpoints is associated
with significantly broadened Si IV line profiles. The line-profile
broadening indirectly indicates the occurrence of numerous EEs below
the transition region (TR), while it directly infers a large velocity
enhancement/perturbation, further causing the plasma flows in the
observed loop system. The observed features are implemented in a
model atmosphere in which a low-lying bipolar magnetic field system
is perturbed in the chromosphere by a velocity pulse with a maximum
amplitude of 200 km s<SUP>-1</SUP>. The data-driven 2D numerical
simulation shows that the plasma motions evolve in a similar manner
as observed by IRIS in the form of flowing plasma filling the skeleton
of a cool-loop system. We compare the spatio-temporal evolution of the
cool-loop system in the framework of our model with the observations,
and conclude that their formation is mostly associated with the velocity
response of the transient energy release above their footpoints in
the chromosphere/TR. Our observations and modeling results suggest
that the velocity responses most likely associated to the EEs could
be one of the main candidates for the dynamics and energetics of the
flowing cool-loop systems in the lower solar atmosphere.
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Title: Exploring Flaring Behaviour on Low Mass Stars, Solar-type
Stars and the Sun
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.; Wyper, P. F.; Scullion,
E.; Wu, K.; McLaughlin, J. A.
2020IAUS..354..384D Altcode:
We report on our project to study the activity in both the Sun and low
mass stars. Utilising high cadence, Hα observations of a filament
eruption made using the CRISP spectropolarimeter mounted on the
Swedish Solar Telescope has allowed us to determine 3D velocity maps
of the event. To gain insight into the physical mechanism which drives
the event we have qualitatively compared our observation to a 3D MHD
reconnection model. Solar-type and low mass stars can be highly active
producing flares with energies exceeding erg. Using K2 and TESS data
we find no correlation between the number of flares and the rotation
phase which is surprising. Our solar flare model can be used to aid
our understanding of the origin of flares in other stars. By scaling
up our solar model to replicate observed stellar flare energies,
we investigate the conditions needed for such high energy flares.
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Title: Observations and 3D Magnetohydrodynamic Modeling of a Confined
Helical Jet Launched by a Filament Eruption
Authors: Doyle, Lauren; Wyper, Peter F.; Scullion, Eamon; McLaughlin,
James A.; Ramsay, Gavin; Doyle, J. Gerard
2019ApJ...887..246D Altcode: 2019arXiv191202133D
We present a detailed analysis of a confined filament eruption
and jet associated with a C1.5 class solar flare. Multi-wavelength
observations from the Global Oscillations Network Group and Solar
Dynamics Observatory reveal the filament forming over several days
following the emergence and then partial cancellation of a minority
polarity spot within a decaying bipolar active region. The emergence
is also associated with the formation of a 3D null point separatrix
that surrounds the minority polarity. The filament eruption occurs
concurrently with brightenings adjacent to and below the filament,
suggestive of breakout and flare reconnection, respectively. The
erupting filament material becomes partially transferred into a
strong outflow jet (∼60 km s<SUP>-1</SUP>) along coronal loops,
becoming guided back toward the surface. Utilizing high-resolution
Hα observations from the Swedish Solar Telescope/CRisp Imaging
SpectroPolarimeter, we construct velocity maps of the outflows,
demonstrating their highly structured but broadly helical nature. We
contrast the observations with a 3D magnetohydrodynamic simulation
of a breakout jet in a closed-field background and find close
qualitative agreement. We conclude that the suggested model provides
an intuitive mechanism for transferring twist/helicity in confined
filament eruptions, thus validating the applicability of the breakout
model not only to jets and coronal mass ejections but also to confined
eruptions and flares.
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Title: Multiwavelength High-resolution Observations of Chromospheric
Swirls in the Quiet Sun
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge,
Philip G.; Doyle, J. G.; Arber, Tony; Scullion, Eamon; Wedemeyer, Sven
2019ApJ...881...83S Altcode:
We report observations of small-scale swirls seen in the solar
chromosphere. They are typically 2 Mm in diameter and last around
10 minutes. Using spectropolarimetric observations obtained by the
CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope,
we identify and study a set of swirls in chromospheric Ca II 8542 Å
and Hα lines as well as in the photospheric Fe I line. We have three
main areas of focus. First, we compare the appearance, morphology,
dynamics, and associated plasma parameters between the Ca II and Hα
channels. Rotation and expansion of the chromospheric swirl pattern
are explored using polar plots. Second, we explore the connection to
underlying photospheric magnetic concentration (MC) dynamics. MCs are
tracked using the SWAMIS tracking code. The swirl center and MC remain
cospatial and share similar periods of rotation. Third, we elucidate
the role swirls play in modifying chromospheric acoustic oscillations
and found a temporary reduction in wave period during swirls. We use
cross-correlation wavelets to examine the change in period and phase
relations between different wavelengths. The physical picture that
emerges is that a swirl is a flux tube that extends above an MC in a
downdraft region in an intergranular lane. The rotational motion of
the MC matches the chromospheric signatures. We could not determine
whether a swirl is a gradual response to the photospheric motion or
an actual propagating Alfvénic wave.
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Title: Observations and MHD modelling of a confined filament eruption
& helical jet
Authors: Fraser Wyper, Peter; Doyle, Lauren; Scullion, Eamon
2019shin.confE.106F Altcode:
To understand how filament eruptions produce coronal mass ejections,
it is useful to understand under what conditions such eruptions fail
to escape the low corona. In this work we used a combination of ground
and space-based observatories to study a small filament eruption that
remained confined within an active region. The filament forms beneath
the domed separatrix of a coronal null point with a closed outer
spine. Soon after the filament starts to erupt, the upward moving
filament material becomes redirected along coronal loops nearby the
outer spine in the form of a helical jet. SST/CRISP captured at high
spatial resolution and temporal cadence the crucial moments when the
transfer of filament material and the development of rotation takes
place, showing this phase in exceptional detail. We compared the
observations with an MHD simulation of a breakout jet in a similar
closed-field topology. In the model the filament channel erupts via
runaway breakout reconnection at the null, launching a confined helical
jet when the erupting flux rope reaches the null and is reconnected
on to overlying coronal loops. This essentially redirects the upward
momentum of the eruption along these loops and back to the surface. We
find excellent qualitative agreement with the observed filament
material evolution and associated loop and surface brightenings in
AIA. We conclude that the breakout jet mechanism provides an intuitive
explanation for such confined eruptions. We gratefully acknowledge
support from an RAS fellowship (PFW) and an STFC studentship (LD).
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Title: Vortex Flows in the Solar Atmosphere: Automated Identification
and Statistical Analysis
Authors: Giagkiozis, Ioannis; Fedun, Viktor; Scullion, Eamon; Jess,
David B.; Verth, Gary
2018ApJ...869..169G Altcode:
Vortices on the photosphere are fundamentally important as these
coherent flows have the potential to form coherent magnetic field
structures in the solar atmosphere, e.g., twisted magnetic flux
tubes. These flows have traditionally been identified by tracking
magnetic bright points (BPs) using primarily visual inspection. This
approach has the shortcoming that it introduces bias into the
statistical analyses. In this work we fully automate the process of
vortex identification using an established method from hydrodynamics
for the study of eddies in turbulent flows. For the first time, we apply
this to detect intergranular photospheric intensity vortices. Using this
automated approach, we find that the expected lifetime of intensity
vortices is much shorter (≈17 s) compared with previously observed
magnetic BP swirls. We suggest that at any time there are 1.48 ×
10<SUP>6</SUP> such small-scale intensity vortices covering about 2.8%
of the total surface of the solar photosphere. Lastly, we compare our
results with previous works and speculate what this could imply with
regards to estimating the global energy flux due magnetic tornadoes
in the solar atmosphere with future higher resolution instrumentation.
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Title: A persistent quiet-Sun small-scale tornado. I. Characteristics
and dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion,
E.; Doyle, J. G.
2018A&A...618A..51T Altcode:
Context. Vortex flows have been extensively observed over a wide range
of spatial and temporal scales in different spectral lines, and thus
layers of the solar atmosphere, and have been widely found in numerical
simulations. However, signatures of vortex flows have only recently
been reported in the wings of the Hα, but never so far in the Hα line
centre. <BR /> Aims: We investigate the appearance, characteristics,
substructure, and dynamics of a 1.7 h persistent vortex flow observed
from the ground and from space in a quiet-Sun region in several
lines/channels covering all atmospheric layers from the photosphere up
to the low corona. <BR /> Methods: We use high spatial and temporal
resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in
several wavelengths along the Hα and Ca II 8542 Å line profiles,
simultaneous Atmospheric Imaging Assembly (AIA) observations in several
Ultraviolet (UV) and Extreme ultraviolet (EUV) channels and Helioseismic
and Magnetic Imager (HMI) magnetograms to study a persistent vortex flow
located at the south solar hemisphere. Doppler velocities were derived
from the Hα line profiles. Our analysis involves visual inspection and
comparison of all available simultaneous/near-simultaneous observations
and detailed investigation of the vortex appearance, characteristics
and dynamics using time slices along linear and circular slits. <BR />
Results: The most important characteristic of the analysed clockwise
rotating vortex flow is its long duration (at least 1.7 h) and its
large radius ( 3″). The vortex flow shows different behaviours in
the different wavelengths along the Hα and Ca II 8542 Å profiles
reflecting the different formation heights and mechanisms of the two
lines. Ground-based observations combined with AIA observations reveal
the existence of a funnel-like structure expanding with height, possibly
rotating rigidly or quasi-rigidly. However, there is no clear evidence
that the flow is magnetically driven as no associated magnetic bright
points have been observed in the photosphere. Hα and Ca II 8542 Å
observations also reveal significant substructure within the flow,
manifested as several individual intermittent chromospheric swirls
with typical sizes and durations. They also exhibit a wide range of
morphological patterns, appearing as dark absorbing features, associated
mostly with mean upwards velocities around 3 km s<SUP>-1</SUP> and
up to 8 km s<SUP>-1</SUP>, and occupying on average 25% of the total
vortex area. The radial expansion of the spiral flow occurs with
a mean velocity of 3 km s<SUP>-1</SUP>, while its dynamics can be
related to the dynamics of a clockwise rigidly rotating logarithmic
spiral with a swinging motion that is, however, highly perturbed by
nearby flows associated with fibril-like structures. A first rough
estimate of the rotational period of the vortex falls in the range of
200-300 s. <BR /> Conclusions: The vortex flow resembles a small-scale
tornado in contrast to previously reported short-lived swirls and
in analogy to persistent giant tornadoes. It is unclear whether
the observed substructure is indeed due to the physical presence
of individual intermittent, recurring swirls or a manifestation of
wave-related instabilities within a large vortex flow. Moreover,
we cannot conclusively demonstrate that the long duration of
the observed vortex is the result of a central swirl acting as an
"engine" for the vortex flow, although there is significant supporting
evidence inferred from its dynamics. It also cannot be excluded that
this persistent vortex results from the combined action of several
individual smaller swirls further assisted by nearby flows or that
this is a new case in the literature of a hydrodynamically driven
vortex flow. <P />The movie associated to Fig. 4 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833101/olm">https://www.aanda.org</A>
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Title: Investigating the rotational phase of stellar flares on M
dwarfs using K2 short cadence data
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.; Wu, K.; Scullion, E.
2018MNRAS.480.2153D Altcode: 2018MNRAS.tmp.1870D; 2018arXiv180708592D
We present an analysis of K2 short cadence data of 34 M dwarfs which
have spectral types in the range M0-L1. Of these stars, 31 showed flares
with a duration between ∼10 and 90min. Using distances obtained from
Gaia DR2 parallaxes, we determined the energy of the flares to be in the
range ∼1.2 × 10<SUP>29</SUP>-6 × 10<SUP>34</SUP> erg. In agreement
with previous studies we find rapidly rotating stars tend to show more
flares, with evidence for a decline in activity in stars with rotation
periods longer than ∼10 d. The rotational modulation seen in M dwarf
stars is widely considered to result from a starspot which rotates in
and out of view. Flux minimum is therefore the rotation phase where we
view the main starspot close to the stellar disc centre. Surprisingly,
having determined the rotational phase of each flare in our study
we find none show any preference for rotational phase. We outline
three scenarios which could account for this unexpected finding. The
relationship between rotation phase and flare rate will be explored
further using data from wide surveys such as NGTS and TESS.
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Title: Convection-driven Generation of Ubiquitous Coronal Waves
Authors: Aschwanden, Markus J.; Gošic, Milan; Hurlburt, Neal E.;
Scullion, Eamon
2018ApJ...866...73A Altcode:
We develop a new method to measure the 3D kinematics of the
subphotospheric motion of magnetic elements, which is used to study
the coupling between the convection-driven vortex motion and the
generation of ubiquitous coronal waves. We use the method of decomposing
a line-of-sight magnetogram from MDI/SDO into unipolar magnetic charges,
which yields the (projected) 2D motion [x(t), y(t)] and the (half) width
evolution w(t) of an emerging magnetic element from an initial depth
of d ≲ 1500 km below the photosphere. A simple model of rotational
vortex motion with magnetic flux conservation during the emergence
process of a magnetic element predicts the width evolution, i.e.,
w(t)/w <SUB>0</SUB> = [B(t)/B <SUB>0</SUB>]<SUP>-1/2</SUP>, and an
upper limit of the depth variation d(t) ≤ 1.3 w(t). While previous
2D tracing of magnetic elements provided information on advection
and superdiffusion, our 3D tracing during the emergence process of a
magnetic element is consistent with a ballistic trajectory in the upward
direction. From the estimated Poynting flux and lifetimes of convective
cells, we conclude that the Coronal Multi-channel Polarimeter-detected
low-amplitude transverse magnetohydrodynamic waves are generated by
the convection-driven vortex motion. Our observational measurements
of magnetic elements appear to contradict the theoretical random-walk
braiding scenario of Parker.
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Title: Signatures of quiet Sun reconnection events in Ca II, Hα,
and Fe I
Authors: Shetye, J.; Shelyag, S.; Reid, A. L.; Scullion, E.; Doyle,
J. G.; Arber, T. D.
2018MNRAS.479.3274S Altcode: 2018MNRAS.tmp.1509S; 2017arXiv170310968S
We use observations of quiet Sun (QS) regions in the Hα 6563 Å, Ca II
8542 Å, and Fe I 6302 Å lines. We observe brightenings in the wings
of the Hα and Ca II combined with observations of the interacting
magnetic concentrations observed in the Stokes signals of Fe I. These
brightenings are similar to Ellerman bombs (EBs), i.e. impulsive
bursts in the wings of the Balmer lines that leave the line cores
unaffected. Such enhancements suggest that these events have similar
formation mechanisms to the classical EBs found in active regions,
with the reduced intensity enhancements found in the QS regions due to
a weaker feeding magnetic flux. The observations also show that the
quiet Sun Ellerman bombs are formed at a higher height in the upper
photosphere than the photospheric continuum level. Using simulations,
we investigate the formation mechanism associated with the events and
suggest that these events are driven by the interaction of magnetic
field lines in the upper photospheric regions. The results of the
simulation are in agreement with observations when comparing the light
curves, and in most cases, we found that the peak in the Ca II 8542
Å wing occurred before the peak in Hα wing. Moreover, in some cases,
the line profiles observed in Ca II are asymmetrical with a raised core
profile. The source of heating in these events is shown by the MURaM
simulations and is suggested to occur 430 km above the photosphere.
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Title: Predictions of DKIST/DL-NIRSP Observations for an Off-limb
Kink-unstable Coronal Loop
Authors: Snow, B.; Botha, G. J. J.; Scullion, E.; McLaughlin, J. A.;
Young, P. R.; Jaeggli, S. A.
2018ApJ...863..172S Altcode: 2018arXiv180704972S
Synthetic intensity maps are generated from a 3D kink-unstable flux
rope simulation using several DKIST/DL-NIRSP spectral lines to make
a prediction of the observational signatures of energy transport and
release. The reconstructed large field-of-view intensity mosaics and
single tile sit-and-stare high-cadence image sequences show detailed,
fine-scale structure and exhibit signatures of wave propagation,
redistribution of heat, flows, and fine-scale bursts. These fine-scale
bursts are present in the synthetic Doppler velocity maps and can be
interpreted as evidence for small-scale magnetic reconnection at the
loop boundary. The spectral lines reveal the different thermodynamic
structures of the loop, with the hotter lines showing the loop
interior and braiding and the cooler lines showing the radial edges
of the loop. The synthetic observations of DL-NIRSP are found to
preserve the radial expansion, and hence the loop radius can be
measured accurately. The electron number density can be estimated
using the intensity ratio of the Fe XIII lines at 10747 and 10798
Å. The estimated density from this ratio is correct to within ±10%
during the later phases of the evolution; however, it is less accurate
initially when line-of-sight density inhomogeneities contribute to the
Fe XIII intensity, resulting in an overprediction of the density by
≈30%. The identified signatures are all above a conservative estimate
for instrument noise and therefore will be detectable. In summary, we
have used forward modeling to demonstrate that the coronal off-limb
mode of DKIST/DL-NIRSP will be able to detect multiple independent
signatures of a kink-unstable loop and observe small-scale transient
features including loop braiding/twisting and small-scale reconnection
events occurring at the radial edge of the loop.
---------------------------------------------------------
Title: Beam electrons as a source of Hα flare ribbons
Authors: Druett, Malcolm; Scullion, Eamon; Zharkova, Valentina;
Matthews, Sarah; Zharkov, Sergei; Rouppe van der Voort, Luc
2017NatCo...815905D Altcode:
The observations of solar flare onsets show rapid increase of hard
and soft X-rays, ultra-violet emission with large Doppler blue shifts
associated with plasma upflows, and Hα hydrogen emission with red
shifts up to 1-4 Å. Modern radiative hydrodynamic models account
well for blue-shifted emission, but struggle to reproduce closely
the red-shifted Hα lines. Here we present a joint hydrodynamic and
radiative model showing that during the first seconds of beam injection
the effects caused by beam electrons can reproduce Hα line profiles
with large red-shifts closely matching those observed in a C1.5 flare
by the Swedish Solar Telescope. The model also accounts closely for
timing and magnitude of upward motion to the corona observed 29 s after
the event onset in 171 Å by the Atmospheric Imaging Assembly/Solar
Dynamics Observatory.
---------------------------------------------------------
Title: Vortex Flows in the Solar Atmoshpere: Automated Identification
and Statistical Analysis
Authors: Giagkiozis, Ioannis; Fedun, Viktor; Scullion, Eamon;
Verth, Gary
2017arXiv170605428G Altcode:
Aims. Due to the fundamental importance of vortices on the photosphere,
in this work we aim to fully automate the process of intensity vortex
identification to facilitate a more robust statistical analysis of
their properties. Methods. Using on-disk observational data of the Fe
I continuum, the process of vortex identification is fully automated,
for the first time in solar physics, with the help of an established
method from hydrodynamics initially employed for the study of eddies
in turbulent flows (Graftieaux et al. 2001). Results. We find that
the expected lifetime of intensity vortices is much shorter (~ 17s)
compared with previously observed magnetic bright point swirls. Our
findings suggest that at any time there are 1.4e6 such small-scale
intensity vortices covering about 2.8% of the total surface of the
solar photosphere.
---------------------------------------------------------
Title: Project SunbYte: solar astronomy on a budget
Authors: Alvarez Gonzalez, F.; Badilita, A. -M.; Baker, A.; Cho,
Y. -H.; Dhot, N.; Fedun, V.; Hare, C.; He, T.; Hobbs, M.; Javed,
M.; Lovesey, H.; Lord, C.; Panoutsos, G.; Permyakov, A.; Pope, S.;
Portnell, M.; Rhodes, L.; Sharma, R.; Taras, P.; Taylor, J.; Tilbrook,
R.; Verth, G.; Wrigley, S. N.; Yaqoob, M.; Cook, R.; McLaughlin, J.;
Morton, R.; Scullion, E.; Shelyag, S.; Hamilton, A.; Zharkov, S.;
Jess, D.; Wrigley, M.
2017A&G....58d2.24A Altcode:
The Sheffield University Nova Balloon Lifted Solar Telescope (SunbYte)
is a high-altitude balloon experiment devised and run largely by
students at the University of Sheffield, and is scheduled for launch
in October 2017. It was the only UK project in 2016 to be selected for
the balloon side of the Swedish-German student programme REXUS/BEXUS
(Rocket and Balloon Experiments for University Students; see box on
p2.25). The success of the SunbYte team in the REXUS/BEXUS selection
process is an unprecedented opportunity for the students to gain
valuable experience working in the space engineering industry, using
their theoretical knowledge and networking with students and technology
companies from all over Europe.
---------------------------------------------------------
Title: High-frequency torsional Alfvén waves as an energy source
for coronal heating
Authors: Srivastava, Abhishek Kumar; Shetye, Juie; Murawski, Krzysztof;
Doyle, John Gerard; Stangalini, Marco; Scullion, Eamon; Ray, Tom;
Wójcik, Dariusz Patryk; Dwivedi, Bhola N.
2017NatSR...743147S Altcode:
The existence of the Sun’s hot atmosphere and the solar
wind acceleration continues to be an outstanding problem in
solar-astrophysics. Although magnetohydrodynamic (MHD) modes and
dissipation of magnetic energy contribute to heating and the mass
cycle of the solar atmosphere, yet direct evidence of such processes
often generates debate. Ground-based 1-m Swedish Solar Telescope
(SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time,
the ubiquitous presence of high frequency (~12-42 mHz) torsional
motions in thin spicular-type structures in the chromosphere. We
detect numerous oscillating flux tubes on 10 June 2014 between 07:17
UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60”
(1” = 725 km). Stringent numerical model shows that
these observations resemble torsional Alfvén waves associated
with high frequency drivers which contain a huge amount of energy
(~10<SUP>5</SUP> W m<SUP>-2</SUP>) in the chromosphere. Even after
partial reflection from the transition region, a significant amount of
energy (~10<SUP>3</SUP> W m<SUP>-2</SUP>) is transferred onto the
overlying corona. We find that oscillating tubes serve as substantial
sources of Alfvén wave generation that provide sufficient Poynting
flux not only to heat the corona but also to originate the supersonic
solar wind.
---------------------------------------------------------
Title: Explosive events in active region observed by IRIS and
SST/CRISP
Authors: Huang, Z.; Madjarska, M. S.; Scullion, E. M.; Xia, L. -D.;
Doyle, J. G.; Ray, T.
2017MNRAS.464.1753H Altcode: 2016arXiv160907698H
Transition-region explosive events (EEs) are characterized by
non-Gaussian line profiles with enhanced wings at Doppler velocities
of 50-150 km s<SUP>-1</SUP>. They are believed to be the signature
of solar phenomena that are one of the main contributors to coronal
heating. The aim of this study is to investigate the link of EEs to
dynamic phenomena in the transition region and chromosphere in an active
region. We analyse observations simultaneously taken by the Interface
Region Imaging Spectrograph (IRIS) in the Si IV 1394 Å line and the
slit-jaw (SJ) 1400 Å images, and the Swedish 1-m Solar Telescope
in the Hα line. In total 24 events were found. They are associated
with small-scale loop brightenings in SJ 1400 Å images. Only four
events show a counterpart in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. Two of them represent brightenings in the
conjunction region of several loops that are also related to a bright
region (granular lane) in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. 16 are general loop brightenings that do
not show any discernible response in the Hα images. Six EEs appear
as propagating loop brightenings, from which two are associated with
dark jet-like features clearly seen in the Hα-35 km s<SUP>-1</SUP>
images. We found that chromospheric events with jet-like appearance
seen in the wings of the Hα line can trigger EEs in the transition
region and in this case the IRIS Si IV 1394 Å line profiles are
seeded with absorption components resulting from Fe II and Ni II. Our
study indicates that EEs occurring in active regions have mostly
upper-chromosphere/transition-region origin. We suggest that magnetic
reconnection resulting from the braidings of small-scale transition
region loops is one of the possible mechanisms of energy release that
are responsible for the EEs reported in this paper.
---------------------------------------------------------
Title: Diagnostics of red-shifted H-alpha line emission from a
C-class flare with full non-LTE radiative and hydrodynamic approach
Authors: Druett, M. K.; Zharkova, V. V.; Scullion, E.; Zharkov, S.;
Matthews, S. A.
2016AGUFMSH31B2563D Altcode:
We analyse H-alpha line profiles with strong redshifts during the
C1.8 flare on 1st July 2012 obtained from the Swedish Solar Telescope
(SST) closely resembling the previous observations (Wuelser and Marti,
1989). The flare has a magnetic field configuration with two levels of
loop structures. The kernels with red shifts are observed in one of the
H-alpha ribbons in the south-west location formed after the main impulse
recorded in the north-east. The locations of H-alpha kernels with red
shifts reveal close temporal and spatial correlation with weaker HXR
signatures and coincide with the locations of coronal jets observed
with AIA/SDO. For interpretation we apply a revised 1D hydrodynamic
and non-LTE (NLTE) radiative model for 5 level plus continuum model
hydrogen atom (Druett & Zharkova, 2016) considering radiative,
thermal and non-thermal excitation and ionisation by beam electrons
with the updated beam densities (Zharkova & Dobranskis, 2016) and
analytical excitation/ionisation rates (Zharkova& Kobylinskijj,
1993). We find the simultaneous solutions of steady state and radiative
transfer equations in all optically-thick lines and continua. The
electron and ion temperatures, ambient density and macrovelocity of the
ambient plasma are derived from a 1D hydrodynamic model with initial
condition of the pre-flaring photosphere for the two fluid ambient
plasma heated by beam electrons (Zharkova & Zharkov, 2007). We
simulate distributions over precipitation depth of ionisation and
departure coefficients for all the hydrogen atom transitions including
the deviation of ionisation from Saha equation affected by non-thermal
electron beams. We show that in the very first seconds after the
beam onset Balmer line profiles are sensitive to the effect of beam
electrons. The combination of the additional ionisation caused by beam
electrons leading to a very strong Stark effect in Balmer lines with
the hydrodynamic heating and formation of a low temperature shock in
the chromosphere is shown to closely account for the visible asymmetric
H-alpha line profiles with strong red shifts observed now and in the
past. The interplay between the ambient plasma heating and non-thermal
collisional excitation and ionisation rates by beam electrons is shown
to define the Balmer line red shifts and continuum enhancements.
---------------------------------------------------------
Title: Observing the Formation of Flare-driven Coronal Rain
Authors: Scullion, E.; Rouppe van der Voort, L.; Antolin, P.;
Wedemeyer, S.; Vissers, G.; Kontar, E. P.; Gallagher, P. T.
2016ApJ...833..184S Altcode: 2016arXiv161009255S
Flare-driven coronal rain can manifest from rapidly cooled plasma
condensations near coronal loop tops in thermally unstable postflare
arcades. We detect five phases that characterize the postflare decay:
heating, evaporation, conductive cooling dominance for ∼120 s,
radiative/enthalpy cooling dominance for ∼4700 s, and finally
catastrophic cooling occurring within 35-124 s, leading to rain
strands with a periodicity of 55-70 s. We find an excellent agreement
between the observations and model predictions of the dominant
cooling timescales and the onset of catastrophic cooling. At the
rain-formation site, we detect comoving, multithermal rain clumps
that undergo catastrophic cooling from ∼1 MK to ∼22,000 K. During
catastrophic cooling, the plasma cools at a maximum rate of 22,700
K s<SUP>-1</SUP> in multiple loop-top sources. We calculated the
density of the extreme-ultraviolet (EUV) plasma from the differential
emission measure of the multithermal source employing regularized
inversion. Assuming a pressure balance, we estimate the density of
the chromospheric component of rain to be 9.21 × 10<SUP>11</SUP>
± 1.76 × 10<SUP>11</SUP> cm<SUP>-3</SUP>, which is comparable with
quiescent coronal rain densities. With up to eight parallel strands
in the EUV loop cross section, we calculate the mass loss rate from
the postflare arcade to be as much as 1.98 × 10<SUP>12</SUP> ±
4.95 × 10<SUP>11</SUP> g s<SUP>-1</SUP>. Finally, we reveal a close
proximity between the model predictions of {10}<SUP>5.8</SUP> K and the
observed properties between {10}<SUP>5.9</SUP> and {10}<SUP>6.2</SUP>
K, which defines the temperature onset of catastrophic cooling. The
close correspondence between the observations and numerical models
suggests that indeed acoustic waves (with a sound travel time of 68 s)
could play an important role in redistributing energy and sustaining
the enthalpy-based radiative cooling.
---------------------------------------------------------
Title: Exploring Coronal Dynamics: A Next Generation Solar Physics
Mission white paper
Authors: Morton, R. J.; Scullion, E.; Bloomfield, D. S.; McLaughlin,
J. A.; Regnier, S.; McIntosh, S. W.; Tomczyk, S.; Young, P.
2016arXiv161106149M Altcode:
Determining the mechanisms responsible for the heating of the
coronal plasma and maintaining and accelerating the solar wind
are long standing goals in solar physics. There is a clear need to
constrain the energy, mass and momentum flux through the solar corona
and advance our knowledge of the physical process contributing to
these fluxes. Furthermore, the accurate forecasting of Space Weather
conditions at the near-Earth environment and, more generally, the
plasma conditions of the solar wind throughout the heliosphere, require
detailed knowledge of these fluxes in the near-Sun corona. Here we
present a short case for a space-based imaging-spectrometer coronagraph,
which will have the ability to provide synoptic information on the
coronal environment and provide strict constraints on the mass, energy,
and momentum flux through the corona. The instrument would ideally
achieve cadences of $\sim10$~s, spatial resolution of 1" and observe the
corona out to 2~$R_{\sun}$. Such an instrument will enable significant
progress in our understanding of MHD waves throughout complex plasmas,
as well as potentially providing routine data products to aid Space
Weather forecasting.
---------------------------------------------------------
Title: Energy Transport Effects in Flaring Atmospheres Heated by
Mixed Particle Beams
Authors: Zharkova, Valentina; Zharkov, Sergei; Macrae, Connor; Druett,
Malcolm; Scullion, Eamon
2016cosp...41E2175Z Altcode:
We investigate energy and particle transport in the whole flaring
atmosphere from the corona to the photosphere and interior for
the flaring events on the 1st July 2012, 6 and 7 September 2011
by using the RHESSI and SDO instruments as well as high-resolution
observations from the Swedish 1-metre Solar Telescope (SST3) CRISP4
(CRisp Imaging Spectro-polarimeter). The observations include hard and
soft X-ray emission, chromospheric emission in both H-alpha 656.3 nm
core and continuum, as well as, in the near infra-red triplet Ca II
854.2 nm core and continuum channels and local helioseismic responses
(sunquakes). The observations are compared with the simulations of
hard X-ray emission and tested by hydrodynamic simulations of flaring
atmospheres of the Sun heated by mixed particle beams. The temperature,
density and macro-velocity variations of the ambient atmospheres are
calculated for heating by mixed beams and the seismic response of the
solar interior to generation of supersonic shocks moving into the solar
interior. We investigate the termination depths of these shocks beneath
the quiet photosphere levels and compare them with the parameters of
seismic responses in the interior, or sunquakes (Zharkova and Zharkov,
2015). We also present an investigation of radiative conditions
modelled in a full non-LTE approach for hydrogen during flare onsets
with particular focus on Balmer and Paschen emission in the visible,
near UV and near IR ranges and compare them with observations. The
links between different observational features derived from HXR,
optical and seismic emission are interpreted by different particle
transport models that will allow independent evaluation of the particle
transport scenarios.
---------------------------------------------------------
Title: Magnetic Flux Cancellation in Ellerman Bombs
Authors: Reid, A.; Mathioudakis, M.; Doyle, J. G.; Scullion, E.;
Nelson, C. J.; Henriques, V.; Ray, T.
2016ApJ...823..110R Altcode: 2016arXiv160307100R
Ellerman Bombs (EBs) are often found to be co-spatial with bipolar
photospheric magnetic fields. We use Hα imaging spectroscopy along with
Fe I 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope
(SST), combined with data from the Solar Dynamic Observatory, to study
EBs and the evolution of the local magnetic fields at EB locations. EBs
are found via an EB detection and tracking algorithm. Using NICOLE
inversions of the spectropolarimetric data, we find that, on average,
(3.43 ± 0.49) × 10<SUP>24</SUP> erg of stored magnetic energy
disappears from the bipolar region during EB burning. The inversions
also show flux cancellation rates of 10<SUP>14</SUP>-10<SUP>15</SUP>
Mx s<SUP>-1</SUP> and temperature enhancements of 200 K at the detection
footpoints. We investigate the near-simultaneous flaring of EBs due to
co-temporal flux emergence from a sunspot, which shows a decrease in
transverse velocity when interacting with an existing, stationary area
of opposite polarity magnetic flux, resulting in the formation of the
EBs. We also show that these EBs can be fueled further by additional,
faster moving, negative magnetic flux regions.
---------------------------------------------------------
Title: High-cadence observations of spicular-type events on the Sun
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T.
2016A&A...589A...3S Altcode: 2016arXiv160108087S
Context. Chromospheric observations taken at high-cadence and
high-spatial resolution show a range of spicule-like features,
including Type-I, Type-II (as well as rapid blue-shifted excursions
(RBEs) and rapid red-shifted excursions (RREs) which are thought to
be on-disk counterparts of Type-II spicules) and those which seem to
appear within a few seconds, which if interpreted as flows would imply
mass flow velocities in excess of 1000 km s<SUP>-1</SUP>. <BR /> Aims:
This article seeks to quantify and study rapidly appearing spicular-type
events. We also compare the multi-object multi-frame blind deconvolution
(MOMFBD) and speckle reconstruction techniques to understand if
these spicules are more favourably observed using a particular
technique. <BR /> Methods: We use spectral imaging observations taken
with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m
Solar Telescope. Data was sampled at multiple positions within the Hα
line profile for both an on-disk and limb location. <BR /> Results: The
data is host to numerous rapidly appearing features which are observed
at different locations within the Hα line profile. The feature's
durations vary between 10-20 s and lengths around 3500 km. Sometimes,
a time delay in their appearance between the blue and red wings of
3-5 s is evident, whereas, sometimes they are near simultaneous. In
some instances, features are observed to fade and then re-emerge at
the same location several tens of seconds later. <BR /> Conclusions:
We provide the first statistical analysis of these spicules and suggest
that these observations can be interpreted as the line-of-sight (LOS)
movement of highly dynamic spicules moving in and out of the narrow 60
mÅ transmission filter that is used to observe in different parts of
the Hα line profile. The LOS velocity component of the observed fast
chromospheric features, manifested as Doppler shifts, are responsible
for their appearance in the red and blue wings of Hα line. Additional
work involving data at other wavelengths is required to investigate
the nature of their possible wave-like activity.
---------------------------------------------------------
Title: High Cadence Observations and Analysis of Spicular-type Events
Using CRISP Onboard SST
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.
2016ASPC..504..115S Altcode:
We present spectroscopic and imaging observations of apparent ultra-fast
spicule-like features observed with CRisp Imaging SpectroPolarimeter
(CRISP) at the Swedish 1-m Solar Telescope (SST). The data shows
spicules with an apparent velocity above 500 km s<SUP>-1</SUP>,
very short lifetimes of up to 20 s and length/height around 3500
km. The spicules are seen as dark absorption structures in the Hα
wings ±516 mÅ, ±774 mÅ and ±1032 mÅ which suddenly appear and
disappear from the FOV. These features show a time delay in their
appearance in the blue and red wings by 3-5 s. We suggest that their
appearance/disappearance is due to their Doppler motion in and out of
the 60 mÅ filter. See Fig. 1 for the evolution of the event at two
line positions.
---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.
---------------------------------------------------------
Title: First simultaneous SST/CRISP and IRIS observations of a
small-scale quiet Sun vortex
Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou,
K.; Scullion, E.; Doyle, J. G.
2016A&A...586A..25P Altcode: 2015arXiv151206032P
Context. Ubiquitous small-scale vortices have recently been found
in the lower atmosphere of the quiet Sun in state-of-the-art solar
observations and in numerical simulations. <BR /> Aims: We investigate
the characteristics and temporal evolution of a granular-scale vortex
and its associated upflows through the photosphere and chromosphere
of a quiet Sun internetwork region. <BR /> Methods: We analyzed high
spatial and temporal resolution ground- and spaced-based observations
of a quiet Sun region. The observations consist of high-cadence time
series of wideband and narrowband images of both Hα 6563 Å and Ca
II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter
(CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well
as ultraviolet imaging and spectral data simultaneously obtained by
the Interface Region Imaging Spectrograph (IRIS). <BR /> Results:
A small-scale vortex is observed for the first time simultaneously
in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the
vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband
images at -0.5 Å, and their corresponding Doppler signal maps, clearly
show consecutive high-speed upflow events in the vortex region. These
high-speed upflows with a size of 0.5-1 Mm appear in the shape of
spiral arms and exhibit two distinctive apparent motions in the plane
of sky for a few minutes: (1) a swirling motion with an average speed
of 13 km s<SUP>-1</SUP> and (2) an expanding motion at a rate of
4-6 km s<SUP>-1</SUP>. Furthermore, the spectral analysis of Mg II k
and Mg II subordinate lines in the vortex region indicates an upward
velocity of up to ~8 km s<SUP>-1</SUP> along with a higher temperature
compared to the nearby quiet Sun chromosphere. <BR /> Conclusions:
The consecutive small-scale vortex events can heat the upper
chromosphere by driving continuous high-speed upflows through the lower
atmosphere. <P />Movies associated to Figs. 2 and 3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527440/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.
---------------------------------------------------------
Title: Observing Cascades of Solar Bullets at High Resolution. II.
Authors: Scullion, E.; Engvold, O.; Lin, Y.; Rouppe van der Voort, L.
2015ApJ...814..123S Altcode:
High resolution observations from the Swedish 1-m Solar Telescope
revealed bright, discrete, blob-like structures (which we refer to as
solar bullets) in the Hα 656.28 nm line core that appear to propagate
laterally across the solar atmosphere as clusters in active regions
(ARs). These small-scale structures appear to be field aligned and
many bullets become triggered simultaneously and traverse collectively
as a cluster. Here, we conduct a follow-up study on these rapidly
evolving structures with coincident observations from the Solar Dynamics
Observatory/Atmospheric Imaging Assembly. With the co-aligned data sets,
we reveal (a) an evolving multithermal structure in the bullet cluster
ranging from chromospheric to at least transition region temperatures,
(b) evidence for cascade-like behavior and corresponding bidirectional
motions in bullets within the cluster, which indicate that there is a
common source of the initial instability leading to bullet formation,
and (c) a direct relationship between co-incident bullet velocities
observed in Hα and He ii 30.4 nm and an inverse relationship with
respect to bullet intensity in these channels. We find evidence
supporting that bullets are typically composed of a cooler, higher
density core detectable in Hα with a less dense, hotter, and fainter
co-moving outer sheath. Bullets unequivocally demonstrate the finely
structured nature of the AR corona. We have no clear evidence for
bullets being associated with locally heated (or cooled), fast flowing
plasma. Fast MHD pulses (such as solitons) could best describe the
dynamic properties of bullets whereas the presence of a multithermal
structure is new.
---------------------------------------------------------
Title: Vortex Identification in the Lower Solar Atmosphere
Authors: Fedun, V.; Giagkiozis, I.; Verth, G.; Scullion, E.
2015AGUFMSH53B2484F Altcode:
Vortices in the solar atmosphere present an ideal driving mechanism
for Alfvenic waves that can efficiently carry energy in the upper
layers of the chromosphere and corona. However, the identification
and classification of vortical motions from observations and numerical
simulations is a challenging task. In this work we leverage a number of
methods conventionally employed in turbulence to identify for the fist
time in the solar atmosphere vortices, in an automated fashion. We also
present a statistical analysis of the properties of the identified
motions and relate this with theoretical results for such magnetic
structures.
---------------------------------------------------------
Title: The Multithermal and Multi-stranded Nature of Coronal Rain
Authors: Antolin, P.; Vissers, G.; Pereira, T. M. D.; Rouppe van der
Voort, L.; Scullion, E.
2015ApJ...806...81A Altcode: 2015arXiv150404418A
We analyze coordinated observations of coronal rain in loops,
spanning chromospheric, transition region (TR), and coronal
temperatures with sub-arcsecond spatial resolution. Coronal rain
is found to be a highly multithermal phenomenon with a high degree
of co-spatiality in the multi-wavelength emission. EUV darkening
and quasi-periodic intensity variations are found to be strongly
correlated with coronal rain showers. Progressive cooling of coronal
rain is observed, leading to a height dependence of the emission. A
fast-slow two-step catastrophic cooling progression is found, which
may reflect the transition to optically thick plasma states. The
intermittent and clumpy appearance of coronal rain at coronal heights
becomes more continuous and persistent at chromospheric heights
just before impact, mainly due to a funnel effect from the observed
expansion of the magnetic field. Strong density inhomogeneities of
0\buildrel{\prime\prime}\over{.} 2-0\buildrel{\prime\prime}\over{.} 5
are found, in which a transition from temperatures of 10<SUP>5</SUP>
to 10<SUP>4</SUP> K occurs. The 0\buildrel{\prime\prime}\over{.}
2-0\buildrel{\prime\prime}\over{.} 8 width of the distribution
of coronal rain is found to be independent of temperature. The
sharp increase in the number of clumps at the coolest temperatures,
especially at higher resolution, suggests that the bulk distribution
of the rain remains undetected. Rain clumps appear organized in
strands in both chromospheric and TR temperatures. We further find
structure reminiscent of the magnetohydrodynamic (MHD) thermal mode
(also known as entropy mode), thereby suggesting an important role of
thermal instability in shaping the basic loop substructure. Rain core
densities are estimated to vary between 2 × 10<SUP>10</SUP> and 2.5×
{{10}<SUP>11</SUP>} cm<SUP>-3</SUP>, leading to significant downward
mass fluxes per loop of 1-5 × 10<SUP>9</SUP> g s<SUP>-1</SUP>, thus
suggesting a major role in the chromosphere-corona mass cycle.
---------------------------------------------------------
Title: Ellerman Bombs with Jets: Cause and Effect
Authors: Reid, A.; Mathioudakis, M.; Scullion, E.; Doyle, J. G.;
Shelyag, S.; Gallagher, P.
2015ApJ...805...64R Altcode: 2015arXiv150305359R
Ellerman Bombs (EBs) are thought to arise as a result of photospheric
magnetic reconnection. We use data from the Swedish 1 m Solar
Telescope to study EB events on the solar disk and at the limb. Both
data sets show that EBs are connected to the foot points of forming
chromospheric jets. The limb observations show that a bright structure
in the Hα blue wing connects to the EB initially fueling it, leading
to the ejection of material upwards. The material moves along a loop
structure where a newly formed jet is subsequently observed in the
red wing of Hα. In the disk data set, an EB initiates a jet which
propagates away from the apparent reconnection site within the EB
flame. The EB then splits into two, with associated brightenings in
the inter-granular lanes. Micro-jets are then observed, extending
to 500 km with a lifetime of a few minutes. Observed velocities of
the micro-jets are approximately 5-10 km s<SUP>-1</SUP>, while their
chromospheric counterparts range from 50 to 80 km s<SUP>-1</SUP>. MURaM
simulations of quiet Sun reconnection show that micro-jets with
properties similar to those of the observations follow the line of
reconnection in the photosphere, with associated Hα brightening at
the location of increased temperature.
---------------------------------------------------------
Title: Stable umbral chromospheric structures
Authors: Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman,
D.; Gallagher, P. T.; Keenan, F. P.
2015A&A...574A.131H Altcode: 2014arXiv1412.6100H
<BR /> Aims: We seek to understand the morphology of the chromosphere in
sunspot umbra. We investigate if the horizontal structures observed
in the spectral core of the Ca II H line are ephemeral visuals
caused by the shock dynamics of more stable structures, and examine
their relationship with observables in the H-alpha line. <BR />
Methods: Filtergrams in the core of the Ca II H and H-alpha lines
as observed with the Swedish 1-m Solar Telescope are employed. We
utilise a technique that creates composite images and tracks the
flash propagation horizontally. <BR /> Results: We find 0.̋15 wide
horizontal structures, in all of the three target sunspots, for every
flash where the seeing is moderate to good. Discrete dark structures
are identified that are stable for at least two umbral flashes, as well
as systems of structures that live for up to 24 min. We find cases of
extremely extended structures with similar stability, with one such
structure showing an extent of 5”. Some of these structures have a
correspondence in H-alpha, but we were unable to find a one-to-one
correspondence for every occurrence. If the dark streaks are formed at
the same heights as umbral flashes, there are systems of structures
with strong departures from the vertical for all three analysed
sunspots. <BR /> Conclusions: Long-lived Ca II H filamentary horizontal
structures are a common and likely ever-present feature in the umbra
of sunspots. If the magnetic field in the chromosphere of the umbra
is indeed aligned with the structures, then the present theoretical
understanding of the typical umbra needs to be revisited. <P />Movies
associated to Figs. 3 and 4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424664/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Small-scale Structuring of Ellerman Bombs at the Solar Limb
Authors: Nelson, C. J.; Scullion, E. M.; Doyle, J. G.; Freij, N.;
Erdélyi, R.
2015ApJ...798...19N Altcode: 2014arXiv1410.5715N
Ellerman bombs (EBs) have been widely studied in recent years due to
their dynamic, explosive nature and apparent links to the underlying
photospheric magnetic field implying that they may be formed by
magnetic reconnection in the photosphere. Despite a plethora of
researches discussing the morphologies of EBs, there has been a limited
investigation of how these events appear at the limb, specifically,
whether they manifest as vertical extensions away from the disk. In
this article, we make use of high-resolution, high-cadence observations
of an Active Region at the solar limb, collected by the CRisp Imaging
SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their
physical properties. The upper atmosphere is also probed using the
Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). We
analyze 22 EB events evident within these data, finding that 20 appear
to follow a parabolic path away from the solar surface at an average
speed of 9 km s<SUP>-1</SUP>, extending away from their source by 580
km, before retreating back at a similar speed. These results show strong
evidence of vertical motions associated with EBs, possibly explaining
the dynamical "flaring" (changing in area and intensity) observed
in on-disk events. Two in-depth case studies are also presented that
highlight the unique dynamical nature of EBs within the lower solar
atmosphere. The viewing angle of these observations allows for a direct
linkage between these EBs and other small-scale events in the Hα line
wings, including a potential flux emergence scenario. The findings
presented here suggest that EBs could have a wider-reaching influence
on the solar atmosphere than previously thought, as we reveal a direct
linkage between EBs and an emerging small-scale loop, and other near-by
small-scale explosive events. However, as previous research found,
these extensions do not appear to impact upon the Hα line core,
and are not observed by the SDO/AIA EUV filters.
---------------------------------------------------------
Title: Erratum: Erratum to: Off-limb (Spicule) DEM Distribution from
SoHO/SUMER Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2014SoPh..289.4749V Altcode: 2014SoPh..tmp..127V
No abstract at ADS
---------------------------------------------------------
Title: Unresolved Fine-scale Structure in Solar Coronal Loop-tops
Authors: Scullion, E.; Rouppe van der Voort, L.; Wedemeyer, S.;
Antolin, P.
2014ApJ...797...36S Altcode: 2014arXiv1409.1920S
New and advanced space-based observing facilities continue to lower
the resolution limit and detect solar coronal loops in greater
detail. We continue to discover even finer substructures within
coronal loop cross-sections, in order to understand the nature of
the solar corona. Here, we push this lower limit further to search
for the finest coronal loop substructures, through taking advantage
of the resolving power of the Swedish 1 m Solar Telescope/CRisp
Imaging Spectro-Polarimeter (CRISP), together with co-observations
from the Solar Dynamics Observatory/Atmospheric Image Assembly
(AIA). High-resolution imaging of the chromospheric Hα 656.28 nm
spectral line core and wings can, under certain circumstances, allow
one to deduce the topology of the local magnetic environment of the
solar atmosphere where its observed. Here, we study post-flare coronal
loops, which become filled with evaporated chromosphere that rapidly
condenses into chromospheric clumps of plasma (detectable in Hα)
known as a coronal rain, to investigate their fine-scale structure. We
identify, through analysis of three data sets, large-scale catastrophic
cooling in coronal loop-tops and the existence of multi-thermal,
multi-stranded substructures. Many cool strands even extend fully
intact from loop-top to footpoint. We discover that coronal loop
fine-scale strands can appear bunched with as many as eight parallel
strands within an AIA coronal loop cross-section. The strand number
density versus cross-sectional width distribution, as detected by CRISP
within AIA-defined coronal loops, most likely peaks at well below 100
km, and currently, 69% of the substructure strands are statistically
unresolved in AIA coronal loops.
---------------------------------------------------------
Title: The Detection of Upwardly Propagating Waves Channeling Energy
from the Chromosphere to the Low Corona
Authors: Freij, N.; Scullion, E. M.; Nelson, C. J.; Mumford, S.;
Wedemeyer, S.; Erdélyi, R.
2014ApJ...791...61F Altcode: 2014arXiv1408.4621F
There have been ubiquitous observations of wave-like motions in
the solar atmosphere for decades. Recent improvements to space- and
ground-based observatories have allowed the focus to shift to smaller
magnetic structures on the solar surface. In this paper, high-resolution
ground-based data taken using the Swedish 1 m Solar Telescope is
combined with co-spatial and co-temporal data from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory
(SDO) satellite to analyze running penumbral waves (RPWs). RPWs
have always been thought to be radial wave propagation that occurs
within sunspots. Recent research has suggested that they are in fact
upwardly propagating field-aligned waves (UPWs). Here, RPWs within a
solar pore are observed for the first time and are interpreted as UPWs
due to the lack of a penumbra that is required to support RPWs. These
UPWs are also observed co-spatially and co-temporally within several
SDO/AIA elemental lines that sample the transition region and low
corona. The observed UPWs are traveling at a horizontal velocity of
around 17 ± 0.5 km s<SUP>-1</SUP> and a minimum vertical velocity
of 42 ± 21 km s<SUP>-1</SUP>. The estimated energy of the waves is
around 150 W m<SUP>-2</SUP>, which is on the lower bound required to
heat the quiet-Sun corona. This is a new, yet unconsidered source of
wave energy within the solar chromosphere and low corona.
---------------------------------------------------------
Title: The Rayleigh-Taylor Instability and the role of Prominences
in the Chromosphere-Corona Mass Cycle
Authors: Berger, Thomas; Liu, Wei; Hillier, Andrew; Scullion, Eamon;
Low, Boon Chye
2014AAS...22421201B Altcode:
We review recent results in the study of so-called "prominence
bubbles", a buoyant instability discovered in quiescent solar
prominences by the Hinode/SOT instrument in 2007. Analysis of the
plasma flows along the boundary of the bubbles indicates that shear
flows leading to Kelvin-Helmholtz instability waves can develop into
the seed perturbations triggering the Rayleigh-Taylor instability. The
non-linear phase of the RT instability leads to the formation of large
turbulent plumes that transport the bubble plasma (and presumably
magnetic flux) into the overlying coronal flux rope. We propose that
the upward turbulent transport of hot bubble plasma and the downflows
of cooler chromospheric plasma in the prominence are related aspects
of a large-scale "chromosphere-corona mass cycle" in which hot plasma
and magnetic flux and helicity from the chromosphere are transported
upwards while the cooler prominence plasma downflows, which decouple
from the magnetic field they are originally frozen-into, represent
the condensation return flows of the cycle. This cycling enables a
mechanism by which magnetic flux and helicity build up in the coronal
flux rope while mass drains out of the flux rope, eventually triggering
a "loss of confinement" eruption in the form of a CME.
---------------------------------------------------------
Title: Are Giant Tornadoes the Legs of Solar Prominences?
Authors: Wedemeyer, Sven; Scullion, Eamon; Rouppe van der Voort, Luc;
Bosnjak, Antonija; Antolin, Patrick
2013ApJ...774..123W Altcode: 2013arXiv1306.2661W
Observations in the 171 Å channel of the Atmospheric Imaging Assembly
of the space-borne Solar Dynamics Observatory show tornado-like
features in the atmosphere of the Sun. These giant tornadoes appear
as dark, elongated, and apparently rotating structures in front of
a brighter background. This phenomenon is thought to be produced
by rotating magnetic field structures that extend throughout the
atmosphere. We characterize giant tornadoes through a statistical
analysis of properties such as spatial distribution, lifetimes,
and sizes. A total number of 201 giant tornadoes are detected in a
period of 25 days, suggesting that, on average, about 30 events are
present across the whole Sun at a time close to solar maximum. Most
tornadoes appear in groups and seem to form the legs of prominences,
thus serving as plasma sources/sinks. Additional Hα observations with
the Swedish 1 m Solar Telescope imply that giant tornadoes rotate as
a structure, although they clearly exhibit a thread-like structure. We
observe tornado groups that grow prior to the eruption of the connected
prominence. The rotation of the tornadoes may progressively twist
the magnetic structure of the prominence until it becomes unstable
and erupts. Finally, we investigate the potential relation of giant
tornadoes to other phenomena, which may also be produced by rotating
magnetic field structures. A comparison to cyclones, magnetic tornadoes,
and spicules implies that such events are more abundant and short-lived
the smaller they are. This comparison might help to construct a power
law for the effective atmospheric heating contribution as a function
of spatial scale.
---------------------------------------------------------
Title: Magnetic tornadoes and chromospheric swirls - Definition
and classification
Authors: Wedemeyer, Sven; Scullion, Eamon; Steiner, Oskar; de la Cruz
Rodriguez, Jaime; Rouppe van der Voort, L. H. M.
2013JPhCS.440a2005W Altcode: 2013arXiv1303.0179W
Chromospheric swirls are the observational signatures of rotating
magnetic field structures in the solar atmosphere, also known as
magnetic tornadoes. Swirls appear as dark rotating features in the core
of the spectral line of singly ionized calcium at a wavelength of 854.2
nm. This signature can be very subtle and difficult to detect given
the dynamic changes in the solar chromosphere. Important steps towards
a systematic and objective detection method are the compilation and
characterization of a statistically significant sample of observed
and simulated chromospheric swirls. Here, we provide a more exact
definition of the chromospheric swirl phenomenon and also present a
first morphological classification of swirls with three types: (I) Ring,
(II) Split, (III) Spiral. We also discuss the nature of the magnetic
field structures connected to tornadoes and the influence of limited
spatial resolution on the appearance of their photospheric footpoints.
---------------------------------------------------------
Title: Interplay of Three Kinds of Motion in the Disk Counterpart
of Type II Spicules: Upflow, Transversal, and Torsional Motions
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.;
Scullion, E.
2013ApJ...769...44S Altcode: 2013arXiv1304.2304S
Recently, it was shown that the complex dynamical behavior of spicules
has to be interpreted as the result of simultaneous action of three
kinds of motion: (1) field aligned flows, (2) swaying motions, and
(3) torsional motions. We use high-quality observations from the
CRisp Imaging SpectroPolarimeter at the Swedish 1-m Solar Telescope
to investigate signs of these different kinetic modes in spicules on
the disk. Earlier, rapid blue-shifted excursions (RBEs), short-lived
absorption features in the blue wing of chromospheric spectral lines,
were identified as the disk counterpart of type II spicules. Here we
report the existence of similar absorption features in the red wing of
the Ca II 8542 and Hα lines: rapid redshifted excursions (RREs). RREs
are found over the whole solar disk and are located in the same regions
as RBEs: in the vicinity of magnetic field concentrations. RREs have
similar characteristics as RBEs: they have similar lengths, widths,
lifetimes, and average Doppler velocity. The striking similarity
of RREs to RBEs implies that RREs are a manifestation of the same
physical phenomenon and that spicules harbor motions that can result
in a net redshift when observed on-disk. We find that RREs are less
abundant than RBEs: the RRE/RBE detection count ratio is about 0.52
at disk center and 0.74 near the limb. We interpret the higher number
of RBEs and the decreased imbalance toward the limb as an indication
that field-aligned upflows have a significant contribution to the
net Dopplershift of the structure. Most RREs and RBEs are observed in
isolation, but we find many examples of parallel and touching RRE/RBE
pairs which appear to be part of the same spicule. We interpret the
existence of these RRE/RBE pairs and the observation that many RREs
and RBEs have varying Dopplershift along their width as signs that
torsional motion is an important characteristic of spicules. The fact
that most RBEs and RREs are observed in isolation agrees with the idea
that transversal swaying motion is another important kinetic mode. We
find examples of transitions from RRE to RBE and vice versa. These
transitions sometimes appear to propagate along the structure with
speeds between 18 and 108 km s<SUP>-1</SUP> and can be interpreted as
the sign of a transverse (Alfvénic) wave.
---------------------------------------------------------
Title: Off-limb (Spicule) DEM Distribution from SoHO/SUMER
Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2012SoPh..280..425V Altcode: 2012SoPh..tmp...88V; 2012arXiv1203.2073V
In the present work we derive a Differential Emission Measure (DEM)
distribution from a region dominated by spicules. We use spectral
data from the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on-board the Solar Heliospheric Observatory
(SoHO) covering the entire SUMER wavelength range taken off-limb in
the Northern polar coronal hole to construct this DEM distribution
using the CHIANTI atomic database. This distribution is then used to
study the thermal properties of the emission contributing to the 171 Å
channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar
Dynamics Observatory (SDO). From our off-limb DEM we found that the
radiance in the AIA 171 Å channel is dominated by emission from the
Fe IX 171.07 Å line and has sparingly little contribution from other
lines. The product of the Fe IX 171.07 Å line contribution function
with the off-limb DEM was found to have a maximum at logT<SUB>max</SUB>
(K)=5.8 indicating that during spicule observations the emission in
this line comes from plasma at transition region temperatures rather
than coronal. For comparison, the same product with a quiet Sun and
prominence DEM were found to have a maximum at logT<SUB>max</SUB>
(K)=5.9 and logT<SUB>max</SUB> (K)=5.7, respectively. We point out
that the interpretation of data obtained from the AIA 171 Å filter
should be done with foreknowledge of the thermal nature of the observed
phenomenon. For example, with an off-limb DEM we find that only 3.6 %
of the plasma is above a million degrees, whereas using a quiet Sun DEM,
this contribution rises to 15 %.
---------------------------------------------------------
Title: Magnetic tornadoes as energy channels into the solar corona
Authors: Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, Oskar;
Rouppe van der Voort, Luc; de La Cruz Rodriguez, Jaime; Fedun, Viktor;
Erdélyi, Robert
2012Natur.486..505W Altcode:
Heating the outer layers of the magnetically quiet solar atmosphere to
more than one million kelvin and accelerating the solar wind requires
an energy flux of approximately 100 to 300 watts per square metre,
but how this energy is transferred and dissipated there is a puzzle and
several alternative solutions have been proposed. Braiding and twisting
of magnetic field structures, which is caused by the convective flows
at the solar surface, was suggested as an efficient mechanism for
atmospheric heating. Convectively driven vortex flows that harbour
magnetic fields are observed to be abundant in the photosphere
(the visible surface of the Sun). Recently, corresponding swirling
motions have been discovered in the chromosphere, the atmospheric
layer sandwiched between the photosphere and the corona. Here we
report the imprints of these chromospheric swirls in the transition
region and low corona, and identify them as observational signatures
of rapidly rotating magnetic structures. These ubiquitous structures,
which resemble super-tornadoes under solar conditions, reach from
the convection zone into the upper solar atmosphere and provide an
alternative mechanism for channelling energy from the lower into the
upper solar atmosphere.
---------------------------------------------------------
Title: New light-travel time models and orbital stability study of
the proposed planetary system HU Aquarii
Authors: Hinse, T. C.; Lee, J. W.; Goździewski, K.; Haghighipour,
N.; Lee, C. -U.; Scullion, E. M.
2012MNRAS.420.3609H Altcode: 2011arXiv1112.0066H
In this work we propose a new orbital architecture for the two proposed
circumbinary planets around the polar eclipsing binary HU Aquarii. We
base the new two-planet, light-travel time model on the result of a
Monte Carlo simulation driving a least-squares Levenberg-Marquardt
minimization algorithm on the observed eclipse egress times. Our
best-fitting model with ? resulted in high final eccentricities for
the two companions leading to an unstable orbital configuration. From a
large ensemble of initial guesses, we examined the distribution of final
eccentricities and semimajor axes for different ? parameter intervals
and encountered qualitatively a second population of best-fitting
parameters. The main characteristic of this population is described
by low-eccentric orbits favouring long-term orbital stability of the
system. We present our best-fitting model candidate for the proposed
two-planet system and demonstrate orbital stability over one million
years using numerical integrations.
---------------------------------------------------------
Title: Small-scale rotating magnetic flux structures as alternative
energy channels into the low corona
Authors: Wedemeyer-Böhm; , Sven; Scullion; , Eamon; Steiner; , Oskar;
Rouppe van der Voort, Luc; de la Cruz Rodriguez, Jaime; Erdelyi,
Robertus; Fedun, Viktor
2012decs.confE..67W Altcode:
Vortex flows are frequently observed in the downflow areas in the lanes
between granules. The magnetic field is advected and trapped by these
flows in the low photosphere. Consequently, the rotation of a vortex
flow is transferred to the atmospheric layers above by means of the
magnetic flux structure. This effect results in so-called swirls, which
are observed in the chromosphere. New simultaneous observations with
the Swedish Solar Telescope and the Solar Dynamics Observatory reveal
that chromospheric swirls can have a coronal counterpart. This finding
implies that the rotating flux structure couples the layers of the solar
atmosphere from the photosphere to the (low) corona. Three-dimensional
numerical simulations confirm this picture and reproduce the swirl
signature. A combined analysis of the simulations and observations
implies that such small-scale rotating flux structures could provide
an alternative mechanism for channeling substantial energy from the
photosphere into the upper solar atmosphere.
---------------------------------------------------------
Title: Type-II spicules: Heating and magnetic field properties from
aligned CRISP/SST and SDO observations
Authors: Scullion, E.; Rouppe van der Voort, L.; de la Cruz Rodriguez,
J.
2012decs.confE..44S Altcode:
Over the past decade there has been a resurgence in the study of
small-scale chromospheric jets known, classically, as spicules. Recent
observations have lead us to conclude that there are two distinct
varieties of spicule, namely, slower type-I (i.e. mottles, dynamic
fibrils, H-alpha spicules etc.) and faster type-II (RBEs: Rapid
Blue-shift Excursions on-disk). Such events dominate the dynamics of
the chromosphere. Joint SDO (Solar Dynamics Observatory) and Hinode
observations have revealed that fast spicules are the source of hot
plasma channelling into the corona. Here we report on the properties
of this widespread heating with observations from the high resolution
CRISP (CRisp Imaging SpectroPolarimeter) instrument at the SST (1-m
Swedish Solar Telescope, La Palma) and co-aligned SDO data. Furthermore,
we reveal new insight into the formation of type-II spicules through
considering the distribution of RBEs with respect to the photospheric
magnetic field (via CRISP).
---------------------------------------------------------
Title: The Response of A Three-dimensional Solar Atmosphere to
Wave-driven Jets
Authors: Scullion, E.; Erdélyi, R.; Fedun, V.; Doyle, J. G.
2011ApJ...743...14S Altcode:
Global oscillations from the solar interior are, mainly, pressure-driven
(p-modes) oscillations with a peak power of a five-minute period. These
oscillations are considered to manifest in many phenomena in the lower
solar atmosphere, most notably, in spicules. These small-scale jets
may provide the key to understanding the powering mechanisms of the
transition region (TR) and lower corona. Here, we simulate the formation
of wave-driven (type-I) spicule phenomena in three dimensions and the
transmission of acoustic waves from the lower chromosphere and into
the corona. The outer atmosphere oscillates in response to the jet
formation, and in turn, we reveal the formation of a circular seismic
surface wave, which we name as a Transition Region Quake (TRQ). The TRQ
forms as a consequence of an upward propelling spicular wave train that
repeatedly punctures and energizes the TR. The steep density gradient
enables the TRQ to develop and radially fan outward from the location
where the spicular plasma column impinges the TR. We suggest the TRQ
formation as a formidable mechanism in continuously sustaining part of
the energy budget of the TR. We present a supporting numerical model
which allow us to determine the level of energy dumping at the TR by
upward-propagating p-modes. Upon applying a wavelet analysis on our
simulations we identify the presence of a chromospheric cavity which
resonates with the jet propagation and leaves behind an oscillatory
wake with a distinctive periodicity. Through our numerical analysis we
also discover type-I spicule turbulence leading to a convection-based
motion in the low corona.
---------------------------------------------------------
Title: A spectroscopic analysis of macrospicules .
Authors: Scullion, E.; Doyle, J. G.; Erdélyi, R.
2010MmSAI..81..737S Altcode:
We explore the nature of macrospicule structures, both off-limb
and on-disk, and their possible relation to explosive events in the
mid-solar atmosphere. We use high resolution spectroscopy obtained with
the SoHO/SUMER instrument. We present a highly resolved spectroscopic
analysis and line parameter study of time series data for such jets. We
focus on two interesting off-limb events which rapidly propagate
between the mid-transition region N IV 765 Å line formation (140
000 K) and the lower corona Ne VIII 770 Å line formation (630 000
K). In one example, a strong jet-like event is associated with a cool
feature not present in the Ne VIII 770 Å line radiance or Doppler
velocity maps. Our data reveals fast, repetitive plasma outflows
with blue-shift velocities of ≈ 145 km s<SUP>-1</SUP> in the lower
solar atmosphere. The data suggests a strong role for smaller jets
(spicules), as a precursor to macrospicule formation, which may have
a common origin with explosive events.
---------------------------------------------------------
Title: Investigating jets in the lower-to-mid solar atmosphere:
Observations & numerical simulations
Authors: Scullion, Eamon
2010PhDT.......557S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Waves in the Transition Region
Authors: Scullion, E.; Erdélyi, R.; Doyle, J. G.
2010ASSP...19..426S Altcode: 2010mcia.conf..426S
Fundamental questions concerning coronal heating and the origin of
the fast solar wind may be answered through greater understanding of
fine structures in the lower solar atmosphere. We present results
from a 2.5-D ideal-MHD simulation from a new numerical code, plus
new supportive observational material. The simulation was run with
the Sheffield Advanced Code (SAC, Shelyag et al. 2008, A&A, 486,
655) and is supported by multi-instrument evidence of a surface wave
obtained from co-alignment of observations with Hinode/EIS and SoHO/MDI.
---------------------------------------------------------
Title: Jets in Polar Coronal Holes
Authors: Scullion, E.; Popescu, M. D.; Banerjee, D.; Doyle, J. G.;
Erdélyi, R.
2009ApJ...704.1385S Altcode:
Here, we explore the nature of small-scale jet-like structures and
their possible relation to explosive events and other known transient
features, like spicules and macrospicules, using high-resolution
spectroscopy obtained with the Solar and Heliospheric Observatory/Solar
Ultraviolet Measurements of Emitted Radiation instrument. We present
a highly resolved spectroscopic analysis and line parameter study
of time-series data for jets occurring on-disk and off-limb in
both a northern and a southern coronal hole. The analysis reveals
many small-scale transients which rapidly propagate between the
mid-transition region (N IV 765 Å line formation: 140,000 K) and
the lower corona (Ne VIII 770 Å line formation: 630,000 K). In one
example, a strong jet-like event is associated with a cool feature
not present in the Ne VIII 770 Å line radiance or Doppler velocity
maps. Another similar event is observed, but with a hot component,
which could be perceived as a blinker. Our data reveal fast, repetitive
plasma outflows with blueshift velocities of ≈145 km s<SUP>-1</SUP>
in the lower solar atmosphere. The data suggest a strong role for
smaller jets (spicules), as a precursor to macrospicule formation,
which may have a common origin with explosive events.
